PROJECT SUMMARY/ABSTRACT This is a revised application. Neuroinflammation has been identified as a major contributing factor to the pathogenesis of Alzheimer?s disease (AD). Studies showing activated microglia surrounding A? plaques in the postmortem AD brain suggest significant involvement of inflammatory pathways in disease progression. PET imaging of AD patients with radio labeled tracers for microglial activation has confirmed these findings. Neuroinflammation involvement of microglia has also been observed in animal models used to study AD. However, the investigation of microglia in AD has been hampered by the lack of specific molecules for understanding microglial phenotype and function and equally as important there is the lack of therapeutic approaches that can target microglia and neuroinflammation. We hypothesize that neuroinflammation is an important target for developing new treatments for AD and that by dampening microglial neuroinflammation with our novel approach (nasal anti-CD3) we will be able to treat AD. We found that nasal anti-CD3 induces an anti-inflammatory immune response that attenuates neuroinflammation in brain-resident microglia cells. In new preliminary data, we found that nasal anti-CD3 improved short-term memory in an AD mouse model. We have found that nasally administered anti-CD3 localizes to cervical lymph nodes where it induces IL-10 secreting T cells that then migrate to the brain and suppress neuroinflammation in microglia. Thus, nasal administration of anti-CD3 is a unique and unexplored target for treating neuroinflammation in AD. The objective of this proposal is to obtain investigate the potential of nasal anti-CD3 to dampen microglia neuroinflammation as a treatment strategy in AD. Aim 1. Investigate the effect of nasal anti-CD3 on microglia phenotype and phagocytic function in aging. Nasal anti-CD3 will be given to 24-month old mice to assess the effect of treatment on in vivo microglia phagocytic function and restoration of microglia homeostasis. We will also measure the induction of IL-10- secreting T cells in the periphery of these mice, which will serve as an easily measured biomarker and on the role of IL-10 on mediating the effect of nasal anti-CD3 on microglia function in aging. Furthermore, we will use IL-10Rflox/floxCX3CR1Cre conditional knockout mice, which do not express the IL-10 receptor on microglia to investigate the role of IL-10 in microglia phagocytic properties as well as its ability to degrade Ab plaques. Aim 2. Investigate the effect of nasal anti-CD3 in the 3xTg AD model. We will perform detailed behavior analysis and neuropathology on 3xTg AD mice treated with nasal anti-CD3 to determine the biological effect and therapeutic potential of anti-CD3. Moreover, we will investigate the effect of nasal anti-CD3 treatment on microglial neuroinflammation in this mouse model of AD using high throughput RNA sequencing (Smart-Seq2).